High power continuous wave light generation at wavelengths different from rare-earth ions (examples of which include but are not limited to Nd, Yb, Er, Ho, Tm) laser lines and their harmonics remains a challenge for current solid-state lasers. Some have approached this challenge by using nonlinear frequency conversion in optical parametric oscillators (OPOs). The prospects for greatly increasing the output power from OPOs, however, may be limited because thermal loading of the nonlinear crystals may result in phase-mismatch and damage. Continuous wave (cw) Raman fibre lasers offer high output powers of 150 W or more at wavelengths different from the laser lines of rare earth doped lasers and their harmonics. Raman fibre laser technology may not be used to shift harmonics of rare earth doped lasers because fibre components, for example integrated fibre grating mirrors, may be very difficult to achieve for high power lasers and due to cumulative damage effects in the fibre such as photodarkening. Subsequent harmonic conversion and/or narrow line width output may be problematic, however, especially in the presence of strong stimulated Brillouin scattering.
Laser systems having within a resonating structure a doped crystalline gain medium and a Raman medium to convert a native frequency of the doped crystalline gain medium have been demonstrated. Increasing the power from these laser systems, for example during continuous wave or quasi-continuous wave operation at infrared wavelengths, has been problematic.